The human MAP Kinase-interacting kinases, also known as MAP Kinase signal-integrating kinases, (MNKs1), are ubiquitously expressed protein-serine/threonine kinases that are directly activated by ERK or p38 MAP kinases.2;3 They comprise a group of four proteins derived from two genes (gene symbols: MKNK1 and MKNK2) by alternative splicing. MNK1a/b and MNK2a/b proteins differ at their C-termini, in each case the a-form possessing a longer C-terminal region than the b-form which lacks the MAP Kinase-binding region. The N-termini of all forms contain a polybasic region which binds Importin α and the translation factor scaffold protein eukaryotic Initiation Factor (eIF4G). The catalytic domains of MNK1a/b and MNK2a/b share three unusual features, two short inserts and a DFD tripeptide feature where other kinases have DFG. Mnk isoforms differ markedly in their activity, regulation, and in subcellular localization. The best-characterized MNK substrate is eIF4E. Although the cellular role of eIF4E phosphorylation remains unclear, it may promote export of a defined set of mRNAs from the nucleus. Other Mnk substrates bind to AU-rich elements that modulate the stability/translation of specific mRNAs.1 MNK1 is highly expressed in hematological malignancies4;5 and both MNK1 and MNK2 are up-regulated in solid tumors such as gliomas and ovarian cancers.6;7 
The Eukaryotic Initiation Factor-4 E (eIF4E) regulates the expression of genes involved in proliferation and survival as a cap dependent mRNA translation and mRNA export factor. eIF4E is dysregulated in several human cancers, including breast,10 prostate,11 and some leukemias,12 and elevated levels of eIF4E are a marker of poor prognosis12;13. Moreover, overexpression and dysregulation of eIF4E leads to an increased tumor number, invasion, and metastases in mouse models13 and transgenic expression of eIF4E leads to a variety of cancers.13;14 
Overexpression of eIF4E results in a specific increase in the translation of these weakly competitive mRNAs, many of which encode products that stimulate cell growth and angiogenesis, e.g., fibroblast growth factor 2 and vascular endothelial growth factor,15-17 cyclin D1,18 and ribonucleotide reductase.19 Several lines of evidence support the key role that eIF4E plays in cancer development and/or progression. First, overexpression of eIF4E can cause neoplastic transformation of cells or accentuate neoplastic features.20;21 Second, reducing eIF4E with antisense RNA or reducing its function by overexpression of the inhibitory 4E-BP proteins can suppress the oncogenic properties of many cell lines.10;22;23 Third, increased expression of eIF4E found in the most classes of solid tumors. These include bladder,24 breast,25;26 cervical,27 head and neck,28-30 and prostate tumors.31 Finally, both the expression and activity of eIF4E are regulated at multiple levels by growth factors and oncogenes,32 suggesting that the protein is a nexus of converging transformation signaling pathways. In addition, there is substantial evidence for de-regulated eIF4E function in neurodevelopmental and psychiatric disorders such as autism, FragileX syndrome and schizophrenia. Mutations in eIF4E and the 4E-BP protein CYFIP1 are associated with autism-spectrum disorders and schizophrenia76-78 and transgenic expression of eIF4E in mice results in autism-related behavioral deficits70. Similarly, loss of 4E-BP2 or CYFIP1 is associated with autism-related phenotypes in mice71-72.
eIF4E is phosphorylated by the MNK1/2 serine/threonine kinases in response to activation by mitogenic and stress signals downstream of ERK1/2 and p38 MAP kinase respectively.2;3 eIF4E phosphorylation at serine 209 by MNK1/2 is required to promote its transformation activity.33;34 Surprisingly, MNK1/2 double knock-out mice do not have any apparent phenotype,35 calling into question whether phosphorylation by MNK has any impact on the functionality of the mammalian eIF4E.36 Nevertheless, MNK phosphorylation of eIF4E on Ser-209 is believed to be critical to eIF4E oncogenic activity.34 
Thus, inhibitors of MNK1/2, by preventing the phosphorylation of eIF4E could provide a viable therapeutic approach in high-eIF4E dependent cancers, neurodevelopmental disorders, and psychiatric disorders.
Studies have shown that overexpression of eIF4E, as well as eIF4E phosphorylation, promote cancer cell survival, at least in part through the elevation of the anti-apoptotic protein Mcl-1.34 Mcl-1 is a Bcl2 family member with a very short half-life, and Mcl-1 mRNA translation highly depends on eIF4E. Thus, it is possible that the inhibition of eIF4E phosphorylation by Mnk might induce the death tumor cells, as shown for Myc-induced lymphoma.34 
Blast crisis chronic myeloid leukemia (BC-CML) is characterized by an expansion of a population of granulocyte macrophage progenitor-like cells (GMPs) that have acquired self-renewal capacity,37 a feature not seen in normal or chronic phase (CP) GMPs. The ability to self-renew is thought to be mediated by β-catenin activation, and may contribute to disease persistence, as well as activity as a reservoir for drug resistance. The mechanisms contributing to β-catenin activation remain obscure, and will need to be identified to improve the control of BC-CML. The role of the translation machinery in mediating β-catenin-mediated self-renewal was investigated, since prior work had implicated aberrant mRNA translation in drug-resistance and BC pathophysiology.38-40 Using immunofluorescence (IF), it was confirmed that BC-GMPs have activated nuclear beta-catenin compared to GMPs isolated from normal cord blood, and that this was associated with increased eIF4E expression and phosphorylation at Ser209. Trough biochemical and genetic approaches in CML cell lines (K562 and KCL22), it was demonstrated that eIF4E overexpression was sufficient to increase beta-catenin activity (as measured by immunofluorescence for nuclear beta-catenin, beta-catenin reporter assays, and expression of beta-catenin-regulated genes). By expressing phospho-mutant forms of eIF4E (S209A, S209D), it was found that the increase in beta-catenin transcriptional activity is dependent on phosphorylation of at Ser209. In line with these observations, siRNA-mediated knockdown or inhibition of the MNK1/2 kinases (which mediate in vivo eIF4E phosphorylation) with small molecules prevented the increased beta-catenin activity induced by eIF4E overexpression. Mechanistically, eIF4E activates beta-catenin signaling via a two-step mechanism. First, eIF4E overexpression increased total cell beta-catenin and secondly, eIF4E phosphorylation facilitated beta-catenin nuclear translocation. The latter step was associated with increased beta-catenin phosphorylation at Ser552, a site known to be involved in nuclear translocation, and directly regulated by AKT. Consistent with this model, siRNA-mediated knockdown or small molecule inhibition of AKT (AKT inhibitor IV) prevented eIF4E-mediated increases in beta-catenin transcriptional activity. The importance of eIF4E phosphorylation on beta-catenin activation and the self-renewal capacity of primary BC GMPs cells was assessed. Treatment with CGP57380, but not imatinib or dasatinib, inhibited eIF4E phosphorylation, as well as prevents accumulation of active nuclear beta-catenin in BC GMPs. The effect of MNK1/2 inhibition was evaluated on the stem cell function of BC cells using both in vitro and in vivo assays. In an in vitro serial replating assay, it was shown that CGP57380 impaired the ability of CD34+ BC cells (including those carrying T315I mutation), but not normal CD34+ cells, to serially replate for more than 8 weeks in methylcellulose. Interestingly, treatment with either imatinib or dasatinib only partially impaired the ability of BC-CML to serially replate. In vitro treatment of BC CD34+ CML cells, but not normal cord blood CD34+ cells, with CGP57380 retarded their ability to engraft NSG mice. Finally, in vivo serial transplantation assay for assessing the leukemia stem cell (LSC) function of patient-derived BC-GMPs was developed. BC GMPs or BC CD34+ CML cells were injected intrafemorally into 8- to 10-week old sublethally irradiated NSG mice. Following engraftment, mice were treated with vehicle, CGP53780 (40 mg/kg/d), or dasatinib (5 mg/kg/d) for three consecutive weeks. Following treatment, human CD34+ cells were isolated from the mice, and transplanted into a second recipient mouse. At 16 weeks, it was found that in vivo treatment with CGP57380, but not dasatinib, prevented BC cells from serially transplanting NSG mice. In summary, these results demonstrate that: 1. eIF4E is overexpressed and phosphorylated at Ser209 in BC, but not in normal GMPs; 2. eIF4E phosphorylation activates beta-catenin signalling in BC GMPs; 3. MNK inhibition prevents eIF4E phosphorylation and beta-catenin signalling in BC GMPs; and 4. MNK inhibition prevents BC GMPs from functioning as leukemia stem cells. These studies suggest that pharmacologic inhibition of the MNK1/2 kinases may be therapeutically useful in BC CML.
The level of expression of eIF4E and the degree of eIF4E phosphorylation is regulated by pathways that include the P38 kinase, MAPK kinase and AKT/mTOR pathways41 as shown in FIG. 4. Inhibitors of mTOR such as rapamycin, decrease the level of phosphorylated eIF4E.42 mTOR inhibitors, as single agents, have proven efficacious in several cancer types such as transplant-associated lymphoma43;44 and Kaposi sarcoma,45;46 tuberous sclerosis-related astrocytoma,47 and mantle cell and other non-Hodgkin lymphomas.48 Two mTOR inhibitors are currently marketed for the treatment of the renal cell carcinoma.49;50 
Inhibition of mTOR by rapamycin also suppresses mTOR catalyzed phosphorylation of EBP1 leading to an increased level eIF4E-EBP1. Consequently, rapamycin inhibits translation initiation by decreasing the phosphorylation of eIF4E-binding proteins, thus decreasing eIF4E availability to the initiation complex.
The treatment with rapalogs typically leads to the clinically stable disease or partial remission rather than the tumor elimination.51 This suboptimal drug effect is likely due at least in part to the cytostatic rather than cytotoxic properties of the mTORC1 inhibitors. Therefore, there is a potential for a drug combination therapy that ideally would culminate in the complete remission of the cancer. However, most of the attempts to combine mTORC1 inhibitors with other drugs, typically the standard chemotherapeutic agents targeting DNA replication, have been disappointing, on occasion even leading to drug antagonism. Preclinical studies of mTOR combined with cis-platin52 or methotrexate53 show the most promise.
Combination therapy with MNK1/2 and mTOR kinases inhibitors could be a viable strategy to treat certain types of cancer.54 WO 2010/055072 discloses MNK and mTOR combination therapy with small molecules, antibodies and siRNA for the treatment of cancer,55 and recent findings support that MNK and mTOR combination induces apoptosis in cutaneous T cell lymphoma cells.42 
Macrophages are major effectors of innate immunity, stimulated by a broad variety of bacterial products through specific TLRs on the cell surface to produce proinflammatory cytokines, such as TNF. E. coli LPS is a potent stimulus to macrophage gene expression, especially TNF, by engaging the TLR4 membrane signaling complex.56 It was shown that TLR signaling pathways require Mnk expression through the use of a panel of commercial TLR agonist panel on macrophage. TNF production was increased as a response to Salmonella LPS (TLR4), ODN2006 (TLR9), HKLM (TLR2), FSL (TLR6/2) and imiquimod (TLR7) stimulation. In each case the production of TNF was inhibited by MNK kinases inhibitor CGP57380 in a dose dependant fashion57 and the release of multiple innate proinflammatory cytokines were affected, supporting a central role for MNK in inflammation.58 
It is reported that heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) when phosphorylated by MNK1/2 accumulates in the cytoplasmic stress granules (SGs) under stress related conditions. hnRNPA1 exit the nucleus bound to poly(A) mRNA and this complex is required for hnRNPA1 phosphorylation by MNK1/2 and for its relocalization to the cytoplasmic SGs. Phosphorylation of hnRNPA1 by MNK1/2 reduces its binding affinity to 3′UTR mRNA and consequently Mnk inhibition enhances hnRNAPA1 association with TNF mRNA. TNF gene transcript level is undetectable in unstimulated T Cell and greatly increased upon stimulation. MNK inhibition effect on TNF appears to be more at the translation level as MNK inhibition has no influence on the level of TNF mRNA.59 Moreover, the formation of SG is reported to be prevented by MNK inhibition60 thus removing the protection that was offered by the SGs where the phosphorylated hnRNPA1 bound mRNA could localize.
MNK inhibitors can regulate the innate immune response in macrophage. A compound with anti inflammatory properties will inhibit the release of pro-inflammatory cytokines.
It has been shown that CGP57380, a Mnk inhibitor, inhibits the release of TNF alpha by macrophage61 (and not eIF4E). According to WO2005/003785 MNK kinases are promising targets for anti-inflammatory therapy.
MNK1/2 were also reported to phosphorylate a number of different proteins in addition to eIF4E. Three of these are hnRNPA1,60 cPLA2 and Sprouty2.62;63 Their role and function is still being investigated. Among these substrates, hnRNPA1 is overexpressed in colorectal cancer and it could contribute to maintenance of telomere repeats in cancer cells with enhanced cell proliferation.64 It is also reported that the expression levels of hnRNPA/B is deregulated in non small cell lung cancer.65 
MNK inhibitors are potentially useful in the treatment of cancers including breast,66 protate,11 hematological malignancies (e.g., CML, AML), head and neck, colon,67 bladder, prostatic adenocarcinoma, lung, cervical, and lymphomas.68;68;69 